Compared with medical imaging diagnostic devices, such as an X-ray diagnostic device and an MRI (Magnetic Resonance Imaging) device, an ultrasound imaging apparatus is a compact device that can display the motion of an object to be tested, such as the pulsatory motion of a heart and the motion of a fetus, in real time with simple operations by putting an ultrasound probe on the body surface.
Specifically, in the ultrasound imaging apparatus, drive signals are supplied to each of a plurality of transducers built in the ultrasound probe, and ultrasonic waves are transmitted to the inside of an examinee. In the ultrasound imaging apparatus, the reflected waves of the ultrasonic waves produced by the difference between the acoustic impedances of biological tissues are received by the plurality of transducers, and an ultrasound image is generated based on the reflected waves received by the ultrasound probe.
Here, in order to improve the image quality of ultrasound images, the ultrasound imaging apparatus controls delay time over drive signals supplied to the plurality of transducers and over reflected wave signals obtained from each of the plurality of transducers.
Specifically, in the ultrasound imaging apparatus, the timing of drive signals supplied to the transducers is controlled based on delay time corresponding to the distance between a predetermined focal point in the inside of the examinee and each of the transducers, and a beam of ultrasonic waves is transmitted to the predetermined focal point in the inside of the examinee.
Based on the delay time corresponding to the distance between the predetermined focal point in the inside of the examinee and each of the transducers, the transducers receive signals from the predetermined focal point differently in terms of time, and the signals are added as their time is matched, i.e. the signals are phased and added. Thus, the ultrasound imaging apparatus generates a line of received signals in focus. As described above, an analog or digital delay circuit is necessary in order to match the signals from a predetermined focal point.
For example, Patent Literature 1 discloses a configuration, in which an echo signal current is accumulated on capacitor banks at a predetermined timing for providing delay time. Patent Literature 2 describes a technique, in which current signals are generated with suitable delay time based on a write pointer and a read pointer from sampled echo signals.